Smooth motor movements at very low speed

sebastian michel said:

- At very low speed the motor rotates not smoothly. The speed is not constant.

What proj_lab# are you using?

For very low speed you need to use a mechanical rotor sensor like an encoder.

The projects that use the encoder are proj_lab12 (velocity) and proj_lab13 (position) under InstaSPIN-MOTION

From everything you have posted I would guess you are trying to do this without your encoder (or at least the SW isn't using your encoder).

Please follow the Lab User's Guide to work sensorlessly through -FOC 5b and then -MOTION 5f, then move to MOTION 12 and 13 of position is required.

Hi,

everything woks well with example proj_lab13, but I do not want to use InstaSPIN-Motion.

My starting point is example proj_lab03 with just InstaSPIN-FOC and without encoder support. I added all the stuff needed by the encoder including the enc module to this example. The next step is to manually set the angle in the estimator before I call CTRL_run(...) in the interrupt handler.

// use encoder position to set estimator angle
_iq angle_pu = ENC_getElecAngle(encHandle);
EST_setAngle_pu(((CTRL_Obj *)ctrlHandle)->estHandle, angle_pu);

// run the controller
CTRL_run(ctrlHandle,halHandle,&gAdcData,&gPwmData);

This works quite well, the motor is running smoothly even at low speed. But there is another problem: The motor has no/little torque in comparison to example proj_lab13. This leads to motor oscillating when speed is set zero.

Is there something I can do to increase the torque?

Sebastian

sebastian michel said:

everything woks well with example proj_lab13, but I do not want to use InstaSPIN-Motion.

Why?

sebastian michel said:

Is there something I can do to increase the torque?

Lack of Torque would come from the angle not being correct, are you doing any sort of zero-ing out the electrical to mechanical alignment?

Lack of Torque could come from the position and velocity controllers not being sufficiently tuned. What are you using, standard cascading PI?

You have some debugging to do.

Hello and thanks for your answer,

I'm using the encoder module in the same way aas it is done in the example proj_lab12

void mainISR()
{
    GPIO_Handle gpioHandle = ((HAL_Obj *)halHandle)->gpioHandle;
    CTRL_Obj *obj = (CTRL_Obj *)ctrlHandle;

    // compute the electrical angle
    ENC_calcElecAngle(encHandle);

    // TODO: remove test code
    static uint_least32_t gLEDcnt = 0;
#define LED_BLINK_FREQ_Hz                      5
#define USER_NUM_PWM_TICKS_PER_ISR_TICK        (3)
#define USER_PWM_FREQ_kHz                      (45.0)
#define USER_ISR_FREQ_Hz                       ((float_t)USER_PWM_FREQ_kHz * 1000.0 / (float_t)USER_NUM_PWM_TICKS_PER_ISR_TICK)
    if (gLEDcnt++ > (uint_least32_t)(USER_ISR_FREQ_Hz / LED_BLINK_FREQ_Hz))
    {
        GPIO_toggle(gpioHandle, GPIO_Number_31);
        gLEDcnt = 0;
    }

    // convert the ADC data
    HAL_readAdcData(halHandle,&gAdcData);

    // use encoder position to set estimator angle
    _iq angle_pu = ENC_getElecAngle(encHandle);
    EST_setAngle_pu(((CTRL_Obj *)ctrlHandle)->estHandle, angle_pu);

    // run the controller
    CTRL_run(ctrlHandle,halHandle,&gAdcData,&gPwmData);


    // write the PWM compare values
    HAL_writePwmData(halHandle,&gPwmData);


    // setup the controller
    CTRL_setup(ctrlHandle);

    // if we are forcing alignment, using the Rs Recalculation, align the eQEP angle with the rotor angle
    if((EST_getState(obj->estHandle) == EST_State_Rs) && (USER_MOTOR_TYPE==MOTOR_Type_Pm))
    {
        ENC_setZeroOffset(encHandle, (uint32_t)(ENC_getPositionMax(encHandle) - ENC_getRawEncoderCounts(encHandle)));
    }
}

At the end if the ISR I also set the zero offset.

Sebastian

I'd look at your position and velocity controllers then.